A derogatory nickname for a Blaster who draws aggro as if they were playing a Tanker. It's a portmanteau of "Blaster" and a word that ends in -tard, but which word depends on whether the actions are deliberate or due to ignorance. Neither word is polite. A more neutral portmanteau would be "Blanker," but since it's really not an effective combination, the term isn't used.
A solo Blastard simply dies a lot, as a Blaster lacks the kind of defenses needed to go wading into an Alpha Strike. It's on teams where the Blastard truly "shines," drawing down enemy fire on the less-well-defended characters before the enemy's attention can be focused on the Tanker. This is especially noxious when the enemy has area of effect attacks.
Sometimes, the Blastard simply doesn't realize yet how aggro works, and assumes that since their attack has a long cast time that others on the team will have engaged the enemy before the attack goes off.
A Blastard need not be a Blaster (or Corruptor), it's more a state of mind. Specifically, the tendency to launch ranged attacks too early in team play and bring negative attention down on the "squishies" of the team. A Tanker with a long-ranged attack can be particularly Blastard-y due to their inherent Taunt.